This invention relates to a feed for a phased array antenna. In particular, the invention relates to a modular feed having a wide operating bandwidth, low system loss, and low complexity.
The capacity of a wireless system may be increased by using phased array antennas in the base stations servicing a wireless service area. In wireless systems employing phased array antennas, the system loss and operating bandwidth associated with the antenna feed network are critical. A high system loss (or, a low system efficiency) in the feed network results in high power requirements in order for the antenna to broadcast at a certain power level. A narrow operating bandwidth of the feed network results in low bandwidth performance of the antenna.
One conventional class of feed network for phased array antennas is the optical space feed. An optical space feed includes a transmitter for transmitting optical signals to an array of pickup horns. The pickup horns are connected to radiating elements for transmitting signals from the phased array antenna. Optical space feeds suffer the significant disadvantages of occupying a large volume, and of having high system losses.
Another class of antenna feed network is the constrained feed. A first type of constrained feed, the series feed, is illustrated in FIG. 3 of U.S. Pat. No. 5,905,462 to Hampel et al. A series feed has a relatively low system loss. However, the operating bandwidth of a series feed is narrow.
A second type of constrained feed is the parallel feed. Parallel feeds may be rendered frequency independent by the use of delays. However, a parallel feed requires a different phase shifting value at each output branch of the antenna, which becomes difficult to achieve in high gain antennas having many parallel output branches. The differing phase shift values also add to the complexity of parallel feeds.
A third type of constrained feed is the corporate feed. Examples of corporate feeds are illustrated in FIGS. 1 and 2 of Hampel et al. As in parallel feeds, a corporate feed""s operating bandwidth may be wide. However, corporate feeds are very complicated, which increases production costs. Corporate feeds also have large system losses because of the multiple bifurcations of the input power supply.
A need therefore exists for a feed, for a phased array antenna, which has a low system loss, a wide operating bandwidth, and low complexity.
The present invention overcomes the disadvantages of conventional feed configurations by reducing both the transmission line length and the number of stages of power bifurcation, which increases the efficiency of the modular feed.
An embodiment of the present invention is a modular feed for a phased array antenna, the modular feed comprising separate modules. A first type of module in the modular feed, the array module, has a series-type feed configuration and thus includes a plurality of radiating element feed lines for connection with radiating elements. A second type of module, the feed module, includes circuitry for feeding signals to a plurality of the array modules. In an exemplary embodiment, a power divider feeds two feed modules, each feed module feeds two array modules, and each array module includes four radiating element feed lines. The use of feed modules to feed the array modules having a series-type feed configuration reduces transmission line length and requires only two stages of power bifurcation.
The array modules may be interchangeable, which decreases the complexity and production costs of the modular feed. The feed modules may also be interchangeable, further decreasing the complexity and cost of the modular feed.